Yes, that's the one. As far as I know, I'm the only guy to ever buy one!
The mod isn't trivial. You'll need to change the filter capacitor stack and
build a FWB rectifier instead of using the original FW doubler. If you raise
the B+ you change the plate impedance and so will have to change the output
tank a by adding some inductance. You'll also have to change the bias on the
tube. For the output tank, the lower the frequency, the more inductance you'll
have to add. 160 m is the toughest to tame; I made a powdered iron toroid
inductor roughly equivalent to the one that's already in there for 160 m and
placed it under the stock large air-dux inductor. It has very high RF voltages
on it and so will need some serious insulation between it and the bottom the
case. I used about 1/4" rubber sheet. You'll then need to move the taps for all
the bands up through through 20 m. I did this by experimentation so that I had
the load and tuning controls where I wanted them (they no longer strictly match
the guide on the front panel). You'll
also have to be very careful tuning it because the RF voltages are much
higher, now. It must never be run lightly loaded as you are certain to flash
over the band switch. Once I figured it out and put stick-on markers for tune
and load pointers, it was easy
I upped the bias on the tube based on the Eimac spec sheet. Failure to do so
will cause the tube to dissipate more than 500 W in an idle condition. I've
forgotten what the new Zener value had to be, but it was a stock value and the
idle bias is set to be (I think, it's been a while) about 60 mA. The primary
requires 240 VAC -- you'll no longer be able to run it on 120 VAC.
Kim N5OP
________________________________
From: R. Eric Sluder-W9WLW <resluder@yahoo.com>
To: "cw_de_n5op@sbcglobal.net" <cw_de_n5op@sbcglobal.net>;
"tentec@contesting.com" <tentec@contesting.com>; "tentec@contesting.com"
<tentec@contesting.com>
Sent: Wednesday, March 5, 2014 11:35 AM
Subject: Re: [TenTec] In praise of older technology
That explains the upgraded Peter Dahl transformer you can still buy for the
AL-80a. I've considered swapping my transformer out because it looks a little
weary for its age and such. I fear a short could be in its windings in the not
to distant future. My amp I believe came from a moist environment, and that is
why I have the concern over a short. The outer paper layers don't look their
best.<br/><br/>Eric<br/>W9WLW<a
href="https://overview.mail.yahoo.com?.src=iOS";><br/><br/>Sent from Yahoo Mail
for iPad</a>
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